The present inventions relate generally to wireless communications antenna systems. In particular, they relate to improvements in dipole arms in multi-band wireless base station antennas.
Developments in wireless technology typically require wireless operators to deploy new antenna equipment in their networks. Disadvantageously, towers have become cluttered with multiple antennas while installation and maintenance have become more complicated. Basestation antennas typically covered a single narrow band. This has resulted in a plethora of antennas being installed at a site. Local governments have imposed restrictions and made getting approval for new sites difficult due to the visual pollution of so many antennas. Some antenna designs have attempted to combine two bands and extend bandwidth, but still many antennas are required due to the proliferation of many air-interface standards and bands.
Ultra-wideband dual-band dual-polarization cellular basestation antennas have been developed. In such ultra wide band antennas, low band elements are interspersed with high band elements. However, low band elements have been observed to distort RF radiation patterns of the high band elements. International Pat. Pub. No. WO 2014100938 A1 (“'938 Application”), titled Dual-band Interspersed Cellular Basestation Antennas, the disclosure of which is incorporated by reference, provides a solution where the low band radiators have dipole arms comprising at least two dipole segments and at least one radiofrequency (RF) choke. The choke is disposed between the dipole segments. Each choke provides an open circuit or high impedance separating adjacent dipole segments to minimize induced high band currents in the low-band radiator and consequent disturbance to the high band pattern. The choke is resonant at or near the frequencies of the high band.
In the '938 Application, each dipole segment comprises an electrically conducting elongated body; the elongated body is open circuited at one end and short circuited at the other end to a center conductor. The electrically conducting elongated body may be cylindrical or tubular in form, and the center conductor connects the short circuited portions of the dipole segments, forming a coaxial choke. Each choke may have a length of a quarter wavelength (λ/4) or less at frequencies in the bandwidth of the high band.
While effective, the choked dipole arms of the '938 Application require multiple manufacturing steps. Each conducting, elongated body is manufactured separately, and affixed to a machined rod center conductor. The rod is machined down where it is not interfacing with a conducting elongated body. Also, each interface between the rod and a conducting elongated body presents a potential for an imperfect ohmic contact, resulting in Passive Intermodulation (PIM).